The present invention is directed to a superplasticizer admixture for hydraulic cement compositions and to the resultant improved hydraulic cement composition. Specifically, the present invention relates to hydraulic cement compositions having certain derivatives of polyacrylic acid polymers, as fully described hereinbelow, which are capable of imparting the combined properties of high flowability to the treated composition, retention of high flowability over a sustained period of time without imparting a significant delay in the initial set time and controlling air voids in the set composition in amounts and of the nature to impart strength and/or durability to the resultant formation.
Hydraulic cements, such as Portland cement, are useful in forming structural formations, such as building members, precast members and the like. These hydraulic cements are mixed with aggregate to form mortars (cement, small aggregate, such as sand, and water) or concrete (cement, small aggregate, large aggregate, such as stone, and water) formations. It is highly desired to increase the flow (slump) properties of the initially formed hydraulic cement composition to aid in placement of the composition and to extend the period of high flowability in order to provide working time to finish the placement of the structure. While extending the period of time that high slump is imparted to a cement composition, it is not desired to have the initial set time significantly delayed as such delay would disrupt the desired work schedule and delay completion of the structural formation.
Increased flowability can be attained by using large dosages of water in the hydrating cement composition. However, it is well known that the resultant cement based structure will have poor compressive strength and related properties which will make it unsuitable as a structural formation. Various additives have been proposed to increase the flowability to hydraulic cement compositions without increasing the water content of the initially formed composition. Such additives have been classified as "cement superplasticizers" and include, for example, compounds such as naphthalene sulfonate-formaldehyde condensates, lignin sulfonates and the like. In certain instances, the superplasticizers have been used as a means of reducing the water to cement ratio in the composition (to enhance the strength of the resultant structure) without detracting from the conventional flow properties or as a means of reducing the water to cement ratio to a lesser degree while still enhancing the flow properties.
More recently, copolymers of alkenyl ethers and acrylic acid or maleic anhydride, and derivatives thereof, have been proposed as agents suitable to enhance slump [Japanese Patent Publication (Kokai) Nos. 285140/88 and 163108/90]. Further, copolymers formed from the copolymerization of hydroxy-terminated allyether and maleic anhydride or the allyether and a salt, ester or amide derivative of maleic anhydride such as disclosed in U.S. Pat. No. 4,471,100 have been proposed as cement admixtures capable of enhancing slump. Still further, U.S. Pat. No. 5,369,198 teaches the use of maleic acid derivatized polymers as a suitable superplasticizer.
In each of the above instances, the proposed cement admixture agents when used in a cement composition do not provide the desired combination of properties or only provide them in low degrees. For example, esterified acrylate copolymers, while providing good slump enhancement, also causes the treated cement composition to exhibit excessive set retardation. In addition, it has been observed that polycarboxylates, such as described in U.S. Pat. No. 5,369,198, provide good slump but may introduce excessive amounts of air to the resultant structural formation. Although a certain degree of air in the form of microbubbles is desired to enhance freeze-thaw characteristics of the resultant structure, excessive air entrainment is not desired as it causes reduction in the strength of the structure formed. Various agents have been proposed to either enhance (air entrainers) or reduce (air detrainers) the air content by counteracting the effects other additives have on a particular cement composition. However, it has been found that the polycarboxylate superplasticizers are not readily mixed with conventional air detraining agents to provide a stable admixture composition. Attempts to form a stable composition has led to the proposal to dissolve certain defoaming agents in a miscible polymer or to disperse microparticles of the agents in the polymer to provide a single composition having the ability to enhance flowability without excessive air entrainment. However, these proposed compositions do not exhibit stability for extended periods. In commercial applications, they would not be stable during extended storage either by the producer and/or at the job site. Any separation would present dosage problems and not achieve the desired result.
It is highly desired to have a single, storage stable cement admixture which when administered to a structural hydraulic cement composition imparts a high degree of slump, causing high slump over an extended period of time, not causing excessive set retardation and providing suitable air entrainment properties to the resultant hydraulic cement structure. It is desired to have a cement admixture capable of providing the slump, set and air entrainment properties which is stable over an extended period from manufacture, storage shipping and job site storage without having the problems of dissociation, separation and the like.